The magnitude of the magnetic moment in the xy plane decays according to

M = M₀[exp(-t/T₂)]

The spin-spin relaxation time T₂ can be measured by using either the

• Carr-Purcell-Meiboom-Gill sequence (the pulse program cpmg ) or,
• One-One Echo sequence (11echo.ts @ the 800MHz spectrometer).

Carr-Purcell-Meiboom-Gill sequence: T2 can be determined by repeating the spin-echo experiment with an increasing number of repeats of the delay-180-delay block, processing the results identically, and plotting peak intensity (logarithmic scale) with respect to the dephasing/spin-echo time. The CPMG experiment yields a signal of intensity

                                  I₀exp(-t/T ₂)             where t  is the total evolution time.
The delay values in the pulse sequence should be much shorter than 1/ J but long enough that the sample should not heat up significantly. The inversion recovery experiment uses the pulse program cpmg and requires a variable loop counter list to provide all the values of the loop counter vc . To create the list, type edlist and select vc from this menu. This calls up a menu of existing vclist  filenames and gives the user the option of creating a new file (‘ Type new name '). Enter the variable loop counter desired.
Use even numbers, to provide cancellation of errors in the 180 pulse. The signal at the receiver is proportional to exp(-2*d20*c/T ₂ )   and therefore can be used to measure T₂ , by acquiring two data sets with different values for c. A 1D spectrum is obtained for each value of c , and the results are stored in a 2D data set.
Although inversion recovery is not technically a 2D experiment, it does generate an array of 1D spectra, which are most easily handled as one 2D file. Thus, the PARMODE must be changed (in eda) into a 2D data set ( PARMODE = 2D ). It should be indicated that the F1 acquisition parameter td should be set to the number of loop counter in the vclist , and the relaxation delay. The spectra can be processed manually by entering xf2.

One-One Echo sequence (Sklenar & Bax, J. Mag. Res . 74, 1987): The method is based on the 11 jump-return sequence and it makes uses of the principles of the spin echo sequence, just with the suppression of the water resonance. The pulse program 11ee.ts appears on our 800 MHz spectrometers. The signal at the receiver is proportional to exp(-2*d4/T₂ )and therefore can be used to measure T₂, by acquiring two data sets with different values for d4 (e.g. 100 µsec and 2.9 msec). The value of T ₂ can be calculated from the ratio of the signals in the two experiments (I₁/ I ₂ ) , given by
exp(5.6/T₂msec) in the above case.